I have this system here I want to replace with BSD, but don't know which flavor to use. Ok, here's the current setup:

Two Debian boxes running (mainly) LDAP, DHCP, postfix, a pop3 and IMAP server (Openexchange). Box 1 is the live system, box 2 is a standby taking over via heartbeat and kept in sync with drbd.

A first idea is to shut off the replication stuff. The linux-people had a lot of problems and I frankly don't see a lot of use in such a setup. The systems have a RAID 5 and the scenario of three disks crashing at once does not really supersede the problems I am afraid of. The 3ware 9500S controller seems to be supported fine. My problem is mainly the drbd part, I haven't found anything about drbd working with OpenBSD or FreeBSD. Heartbeat is available.

I thought about a setup with device two being an empty machine. Device 1 will be monitored by two other machines in the network. In case of an error, an immediate message is sent to an administrator, who will turn the broken machine off, swap the SATA drives from the raid into the spare machine and turn it back on (where the OS will fetch the current /etc stuff etc. from the raid and copy it to the local machine, keeping that part in sync. No immediate takeover yes, but my opinion is, a stable system does not need such a redundant. The current linux stuff is crashing a lot plus it is not really equipped with a reliable takeover (it needs a real network crash before the second machine takes over). If anything else falls apart, maybe we could use a mysql db to store the email data of 500G, but should be able to handle 2T as well.

So my questions:

1. Does something like drbd (www.drbd.org) exist for OpenBSD/FreeBSD?
2. If so, is it reliable and performant?
3. Can the postfix/mysql combo be recommended for OpenBSD/FreeBSD?
4. Any other recommendations?

Hope someone has experience with those questions and gives some input?

CARP is also available for FreeBSD (carp(4)), and possibly FreeBSD. There's VRRPD as well, which I believe is also available for Linux.

However, CARP is more of a replacement for heartbeat than for drbd, as it just provides a virtual/shared IP and will fail-over the network connection, and not the disk. ggate+gmirror would be closer to drbd.

But still, it's not like drbd. Anyways, I figured that I need dbmail to store the mail itself in a mysql database, am I right? Because with everything in a MySQL db I could leave the replication to MySQL instead of messing around with drbd?

The Common Address Redundancy Protocol, you could say is like RAID for your network hosts. You can have multiple hosts sharing a set of IP, let's say you've got a master MySQL server that replicates its data to a pair of slave servers, one for backup and one on hot standby to be swapped out with the master in the event of doomsday. Then all of a sudden your master servers disk eats itself, and you've only got the slave servers! With CARP, you should be able to have your network setup so the mysql slave server on hot standby takes over for the master, rather then making clients wait until you manually get her servicing the masters requests.